Recently, a demand for a micro three-dimensional measurement and inspection equipment has increased in laboratories or industries. In particular, with the increased tendency of miniaturization and high integration in a semiconductor production process, a demand for a three-dimensional inspection equipment that can measure a structure in a nano unit or less has rapidly increased. An electron microscope, an atomic force microscope, and the like, has been restrictively used due to a slow speed and therefore, a technology of optically measuring a shape like an interferometer has been mainly used widely in a production process. As representative optical shape measuring methods, there are a chase shifting interferometer, (hereinafter, referred to as PSI), a white-light scanning interferometer (hereinafter, referred to as WLSI), a confocal microscope, and the like.
Among the optical measuring methods, the PSI can measure a shape of a surface with a resolution within a nanometer, but may have a disadvantage in that a measurement region is limited to a ¼ wavelength height smaller than a 1 wavelength. Therefore, the PSI has been widely used in the case of measuring a smooth curved shape having a wide area like a surface of a mirror. FIG. 1 is a diagram for describing a method of measuring a shape of a surface by making up a Twyman-Green interferometer. Light oscillated in a light source 1 transmits a lens 2 and then, transmits a beam splitter 3 or is reflected therefrom. The transmitted light is incident to a reference mirror 4, the incident light is again reflected therefrom, and the reflected light is incident to the beam splitter 3. The light reflected from the beam splitter 3 is incident to a measurement object 5, the incident light is again reflected from the measurement object 4, and the reflected light is incident to the beam splitter 3. As such, the light again incident to the beam splitter 3 is re-transmitted or re-reflected to acquire an interference fringe image 6 under different phase conditions, phases Φ (x, y) at each point can be obtained by analyzing the interference fringe image 6, and the shape of the measurement object can be known by analyzing the obtained phases.
A basic principle of the interferometer splits a single light into two lights by a light splitter, wherein one of the two lights is used as a reference light and the remaining one is used as an object light, the object light reflected by inputting light to the measurement object interferes with the reference light to acquire the interference fringe, and the surface information of the measurement object is obtained by analyzing the interference fringe. In order to obtain the phases Φ (x, y), several sheets of images are required. Therefore, various methods for rapidly and accurately obtaining the phases F (x, y) have been proposed. As one of the methods, a method for obtaining a phase using a sheet of image has been proposed. The method has an advantage of more rapidly obtaining a phase than other methods requiring several sheets of images. However, when intending to measure a discontinuous surface of a step-like shape, the method has a common disadvantage of the PSI that the measurement region may be limited to a ¼ of a wavelength.
As a method for expanding the measurement region, a method for implementing a PSI using two or more wavelengths has been known. Generally, phase information is first obtained by measuring a shape using a single wavelength λ1 and is then obtained using a second wavelength λ2, thereby expanding the measurement region using two kinds of information. The method requires a minimum of double measurement time and therefore, a need exists for a new method for implementing a high-speed measurement.